The only real permadraws are made out of cables and have steel biners, right?

Personally, I prefer chain for draws that rub (e.g. over a roof) but the decision whether to go with chain or cable depends on consensus in your area. The only solution I would *not* go with is just replacing the nylon over and over until someone falls on it and it breaks.

3rd permadraw on crash and burn is rubbing on the rock and wearing through the fabric. What is the protocol for replacing it?

you replace it with a good one.

I think what kennoyce means is that you replace it with a good one after obtaining approval from the local Permadraw Replacement Committee, who shall, after a public comment period of not less than 60 days, render a decision on whether to replace the permadaw, which decision shall require a majority vote of the members of the Committee, except in the case that an objection to the replacement of said permadraw has been duly communicated in writing to the Committee by at least three bona fide members of the local climbing community, in which case approval shall require the assent of at least two-thirds of the members of the Committee.